This project involves the conduct of therapeutic clinical trials for the treatment of X-linked chronic granulomatous disease with autologous blood stem cell targeted gene therapy. Patients with CGD have defective circulating blood neutrophils that fail to produce microbicidal hydrogen peroxide. They suffer from recurrent life threatening infections and premature mortality. About six years ago we completed a clinical trial of gene therapy for the inherited deficiency of the phagocytic cell immune system known as the X-linked form of chronic granulomatous disease (X-CGD). In some of our gene therapy treated patients up to 1 in 400 circulating neutrophils in the peripheral blood demonstrated functional correction following the gene therapy. This peak level of correction occurred at 3 to 6 weeks after therapy and the effect could be sustained for over a year in three of five patients treated with multiple infusions of autologous ex vivo gene corrected CD34+ progenitor cells. These gene therapy studies demonstrated that it is possible to provide a low level partial and transient correction of the CGD defect in patients by gene therapy. In 2004, the results of a similar gene therapy trial for CGD was reported by a group from Germany that treated X-CGD patients; however they also included the chemotherapy agent busulfan at a dose of 8mg/kg to make room in the bone marrow and therefore improve engraftment. They achieved initial levels of 20% in the peripheral blood however, there was also an outgrowth of gene corrected myeloid cells resulting in increasing levels. This outgrowth was however associated with oligoclonality and over-representation of clones in which the gene therapy vector had by insertional mutagenesis activated MDS1 and other genes associated with myeloid cell development. Our own insertional analysis of myeloid blood cells from our own previous CGD gene therapy study demonstrated significant polyclonality and no eveidence of outgrowth of clones containing vector insertion in MDS1 or other myeloid regulatory genes. Cause for the differences between the recent German X-CGD gene therapy study and our own previous studies in this regard may relate to the strong promoter activity known to be associated with their murine spleen focus forming virus based vector relative to our MFGS which is derived from murine Moloney leukemia retrovirus. Although the patients in this trial were not cured, and the first patient actually expired from sepsis, both patients did have some clinical benefit from the treatment. Both patients had an underlying infection at the time of their transplant which resolved in the initial peritransplant period prior to the clonal outgrowth and ultimate silencing of the transduced cells.[unreadable] We have in this year begun enrolling patients on our own new gene therapy trial (Protocol 07-I-0017) for the treatment of patients with XCGD who have an underlying infection not amenable to cure by standard therapies. Based on preclinical data in the rhesus as well as clinical data in a patient, we are using busulfan at a dose of 10mg/kg prior to infusion of the gneentically modified cells. To date we have treated two patients, the first a 28 year old male with multiple liver abscesses, not amenable to surgical or radio frequency ablative approaches. The patient initially had a level of 24% positive cells and at 7 months post treatment had resolution of his liver abscesses, with 1.2% detectable marking persisting in the peripheral blood. Most recently he developed a line infection and as a result seeded his liver with a staph aureus, distinct from the original infection. He has responded to oral antibiotics and overall continues to do well with much fewer infections that in the past. His marking level is still detectable at 9 months post transplant and there is no evidence of clonal outgrowth. The second patient was treated due to an underlying fungal infection of the chest wall. Despite almost three years of ongoing polymicrobial therapy, this lesion has persisted, and therefore the patient was eligible for the gene therapy protocol and enrolled in June of this year. His course, however, was not as successful as he appears to have developed an immune reaction against the transduced cells, with rapid clearance of transduced cells one week after initially having 5% marking in the peripheral blood. This patient is now being worked up for a matched unrelated cord blood transplant.